1. Field of the Invention
The invention relates to thermoset fiber-reinforced molded articles having in-mold applied coatings.
2. Description of the Prior Art
MATCHED METAL MOLDING--Fiber-reinforced, thermosetting resinous products are produced in elevated temperature, matched metal molds. One of the shortcomings of this process is that the molded article surface tends to be irregular and tends to have surface exposure of the reinforcing fibers, usually glass fibers.
IN-MOLD COATINGS--The in-mold coating technique has been developed to improve the quality of the surface of a molded article after the curing of the article in a matched metal mold has been substantially advanced, U.S. Pat. No. 4,081,578. In the matched metal molding process, two or more shaped mold elements cooperate to define a mold cavity. A molding composition (polymerizable thermosetting resin and fibrous reinforcing material and usually fillers, catalysts, mold release agents, and other reagents) is introduced into a mold cavity between the matched metal mold surfaces. The shaped mold elements are brought together to spread the molding composition throughout the mold cavity and to confine the molding composition until curing is essentially completed. The heated mold elements initiate polymerization. When the polymerization is well advanced, i.e., the article has assumed the shape of the mold cavity, the mold surfaces are separated slightly, usually a distance from 3 to 40 mils, and a liquid, in-mold, coating composition is injected under pressure into the mold cavity. Thereafter the mold elements are again brought together under pressure which causes the liquid coating composition to disperse over the surface of the partially cured article and to conform with the surface of the contiguous mold element. After a suitable time, the polymerization of the article is essentially completed and the polymerization of the coating composition is essentially completed. At that time the mold elements are separated and the coated, molded article is removed.
Two-component in-mold coating compositions are known, U.S. Pat. No. 4,081,578, which employ polyisocyanates as one ingredient and employ hydroxy-terminated high molecular weight unsaturated polyester resin as another ingredient. These compositions have limited pot life after being mixed and must be used promptly. These compositions have exhibited some inadequate adhesive properties.
There is a demonstrated need for a single-component coating composition which can be prepared and retained for extended periods of time by the molding operator.